Paper is used for a great many things, from paper towels and tissues through sheets of paper for printing at home or work, to special paper for banknotes, and each different use needs a different kind of paper with different properties. Manufacturers have to test their paper for these properties, and one is ‘tensile strength’, the strength of the paper, both wet and dry.
Testing It Out
Make sure that the samples that you are testing for strength are all the same size – one way to do this is to stretch the piece of paper over a circular frame used for embroidery. If wetting the paper, use the same amount for each test, and give it time to soak in.
To test for strength, put small weights (perhaps coins) on the paper one at a time and record the type of paper, whether it’s tested wet or dry, and how much weight the paper can hold before tearing. Think about what the paper is designed for – does the strength match up to the purpose?
As these are designed for mopping things up, test them for strength when they are wet as well as when they are dry. Try different brands – are the cheapest own-brand or basic paper towels the weakest, and does the strength of the towels match up with the advertising? Are they stronger when they are wet or dry? Does it make any difference whether it is recycled or not? Try this with tissues as well – does it make a difference whether the tissues are two ply or three ply?
Use pieces of paper cut out of different kinds of paper bags. Is white paper any stronger than brown paper?
Writing and Printing Paper
Try different kinds of paper designed for different kinds of writing, drawing and printing.
Papers to test:
- Paper from an exercise book
- Good quality writing paper
- Recycled lined paper
- Non-recycled lined paper
- Sketch pad paper
- Magazine paper
- Printer paper
Make some recycled homemade paper (see ‘The Science of Recycling’) – how strong is this compared with bought paper?
Paper is made from interlocking fibres that are originally from wood. Overall, recycled paper isn’t as strong as paper made from new wood pulp (known as virgin paper), because the fibres become shorter each time the paper is recycled. Paper can be recycled about five to seven times, but usually some new wood pulp is added during the recycling process to make the paper stronger.
Some paper towels have extra chemicals added to them to improve their wet strength and how much water they absorb. This should mean that they will hold more weight before breaking than the more basic brands.
Paper bags have to be strong enough to take the weight of the goods inside – so a small paper bag designed for 100 g of sweets won’t be as strong as a paper bag for grocery shopping.
With paper for writing and printing, generally the cheaper quality paper will have less strength. Paper for newspapers has to be cheap enough to keep the cost of an individual paper down, and only has to last for one day (does leaving newspaper out in the sun for a couple of days change its strength?) Magazines tend to cost more and are more likely to be kept for days or weeks, so need to be on stronger paper.
Printer paper has to be strong enough to withstand the stresses of being pulled through an inkjet or laser printer at home or in the office.